The present invention relates to a powder regulating method and apparatus for a spraying device for spraying a powdered coating on articles, and more particularly to a method and apparatus for measuring and regulating the flow rate of the powder in a powder spraying system.
A device of this type is known from Federal Republic of Germany Pat. No. 28 49 295. In the known device, a pressure regulator is located in each of a gas feed line and a gas control line. The gas lines supply streams of gas to a venturi injector to cause the injector to draw powdered coating material from a powder container. From the injector, the powdered material, admix with gas, is fed through a powder feeding tube to a spraying head for being sprayed on an article.
A powder regulating instrument, disposed within the powder feeding tube, measures the flow rate of the powder, compares it to a set powder flow rate value, and controls the gas pressure in the gas lines to cause the measured powder flow rate to follow the set value. In this known arrangement, the powder regulating instrument measures either the velocity of the powder/gas mixture or the proportion of powder to gas.
An injector based powder feeding device in which powder is conveyed pneumatically by means of a stream of gas is described in United States Pat. No. 3,504,945.